This invention relates to a gas water heater. More particularly, the invention relates to a thermodynamically activated flue damper for a gas water heater. Even more particularly, the invention relates to the use of thermally sensitive material to activate the flue damper of a gas water heater.
Historically, the energy efficiency of gas water heaters has been limited by the use of an open flue tube design. Heat energy is extracted in these systems from the hot water by the air that is drafted up the open flue tube. The loss of thermal energy attributable to the flue draft typically accounts for 50% or more of the total energy loss during the off cycle phase of water heater operation.
It has long been known that closing the flue in a gas water heater when the burner is in its off cycle will help to minimize the energy losses described above. This has been addressed in the systems of the prior art through the use of a damper or other flue-obstructing device. An electric motor or solenoid is typically used as an engine, and is controlled by an electrical or electronic logic system.
However, these systems have the significant disadvantages that they require a complicated sensing and control system to operate the damper and that they require a source of electricity to power the unit. Consequently, these systems are expensive to manufacture, are often unreliable, and will not operate if there is a loss of power.
It has generally been known in the prior art to utilize thermally responsive materials to operate a damper. For example, examples of standard vent dampers that utilize thermally responsive materials are disclosed in U.S. Pat. Nos. 4,838,481; 4,460,121; and 4,236,668. However, because of important safety concerns in the operation of gas water heaters, the American National Standard Institute (ANSI) has strict regulations on the design and operation of both flue dampers and vent dampers, which have very different operational concerns. For example, ANSI Rule 1.27.10 requires that vent dampers assume their open position in the event of motive power failure, unless interlocked with the gas ignition system to prevent its operation when the damper is not fully open.
Unfortunately, these vent dampers are not usable within the flue of a gas water heater, since they do not satisfy the aforementioned regulations for flue dampers, such as their ability to be removed for cleaning.
Vent dampers utilizing thermally responsive materials are also known in the art. One example of such a system of the prior art is disclosed in U.S. Pat. No. 5,186,385. As disclosed therein, a hinged damper is attached to bimetallic springs, which operate the damper as hot air enters the vent. Similar bi-valve vent systems are also disclosed in U.S. Pat. Nos. 5,695,116 and 4,441,653.
However, these systems have the distinct disadvantage that they cannot be used in the flue of gas water heaters, because of the significant flue obstruction caused by the bi-valve design. These hinged devices must also be fastened to the wall of the flue, which prevents their removal for the cleaning of water heater flue, as required by the aforementioned regulations. Moreover, the conventional bimetallic strips used in these systems cannot stand up to the corrosive elements present in the hot flue gases of today""s gas water heaters.
Accordingly, a system of minimal complexity and maximum reliability is needed for reducing thermal losses through the flue of a gas water heater without the use of electrical or electronic control systems, and which complies with the specific safety requirements of gas water heaters.
The invention is directed to a flue damper system for controlling the passage of exhaust gases through the flue of a gas water heater with a thermally responsive material in conjunction with a pivoting flue damper that is mounted to a support member within the flue of the gas water heater. The thermally sensitive member is connected between the flue damper and the support member in the flue to control the pivoting of the flue damper as the thermally sensitive metal expands or contracts at the transition temperature. The flue damper system may also include a counter-balancing member to provide a counter-balancing force to the thermally sensitive metal, such as a coil spring. The thermally sensitive member may be formed in the shape of one or more from the group consisting of a rod, a wire, and an elongated bar, and may comprise Nytinol or other similar metal alloys.